Semidwarf and Standard‐Height Cowpea Responses to Row Spacing in Different Environments

Yield potential of several grain crops has been increased by breeding semidwarf cultivars with greater harvest index and growing them at high plant densities. We evaluated effects of the semidwarf trait on yield potential of cowpea [ Vigna unguiculata (L.) Walp.] in contrasting, but productive, environments. Three semidwarf and three standard‐height cowpea lines with similar indeterminate habits and phenology were evaluated at row spacings of 51, 76, and 102 cm in four field environments where the extent of early vegetative vigor varied. Main stems of semidwarf lines were 33% shorter, and they produced 13% less vegetative shoot biomass than standard lines. Average grain yield of semidwarf lines was 10% greater than that of standard lines and was associated with 11% higher harvest index and 19% greater pod set. Semidwarf lines produced relatively greater yield than standard lines at narrower row spacings (15, 11, and 4% greater than standard lines at 51, 76, and 102 cm row spacing, respectively). Average yield of standard lines did not respond to row spacing. In a stressful soil environment that caused extreme dwarfing of both plant types, there was no difference in grain yield between semidwarf and standard lines. Semidwarf lines produced greater yield than standard lines at narrow row spacing in soil conditions that promoted moderate to vigorous early plant growth due to impaired reproduction of standard, but not semidwarf, lines when competition for light was strong.